Agatha's Soul Cauldron + Walking Ballista + Evernight Shade

Agatha's Soul Cauldron

Walking Ballista

Evernight Shade

How it works

1. Activate Evernight Shade using Walking Ballista's second ability by removing a +1/+1 counter from it.
2. Repeat step 1 until Evernight Shade has no +1/+1 counters on it.
3. Resolve all Evernight Shade abilities dealing 1 damage to Evernight Shade, and any remaining damage to any target(s).
4. Evernight Shade dies as a state-based action due to having 0 toughness.
5. Evernight Shade's undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
6. Repeat.

This loop transforms a modest shade and a modular construct into an infinite engine, all mediated by a bubbling cauldron of exiled potential. With Evernight Shade safely in the graveyard, Agatha's Soul Cauldron grants its activated pump ability to any creature bearing a +1/+1 counter, while its mana-filtering trait ensures you can always pay the black activation cost. When you place Walking Ballista into the mix, its ability to remove counters conveniently fuels Evernight Shade's pump ability over and over again without actually needing black mana. By stripping away its own toughness until it perishes, Evernight Shade triggers its own undying ability to return to the battlefield fresh, ready to loop endlessly and secure your victory.